236 XIFE OF The weariest part of the ascent was the entourage of the mountain, which consists of rocks and chasms continuing up to the snow boundary. This boundary begins already at an elevation of 2460 toises, and is -533 toises broad to the crater. It was not possible for Humboldt to reach the brim of the crater. On the south-western side the regularity of the cone is broken by a mass of rock half buried in the snow, which the natives call the head of the Inca. It is said to have been originally the real point of the Goto- paxi, but to have been blasted and thrown down at its first eruption. As lie could go no further on this side, Humboldt went to the volcano of Aiitisaiio, to reach the utmost practicable height of the extreme point of the Ohini- borazo. He and his companions had already ascended to .a height which before them no one had reached, when, on the 23rd June, 1802, he arrived on the Ohimborazo, and succeeded in bringing the instruments so high. He was then 3036 toises above the level of the sea, and suffered the consequences of the great rarefica- tion of the air. The thermometer stood still, as the mercury in it had frozen, and as mercury only freezes at 32 degrees Reaumur, or 40 degrees Celsius, the xeader may form an idea of the cold to which Hum- boldt and his companions were exposed. The rarefied air made respiration very difficult; and as the circu- lation of the blood in .the human body reqxiires a pressure of air from without, to impart a certain de- gree of imperviousness to all the fibres and veins, the bold travellers soon felt the want of this pressure by the blood flowing from their eyes, lips, and gums. But in sight of the extreme point of Chimborazo, only 224* toises higher, the difficulty of respiration and the flow of blood could not deter Humboldt from con- tinuing his journey. Nature, however, drew a boun- dary to oppose the progress of the courageous man. A broad, insurpassable chasm gaped before him, and separated him physically from the top of the Chim- towering proudly above him.